This invention relates to lasers and more particularly to organic dye lasers.
In recent years, organic dye lasers have become important tools for spectroscopy, photochemistry, and laser isotope separation. These and other applications are discussed by T. W. Hansch in "Applications of Dye Lasers," chapter 5 of Dye Lasers, F. P. Schafer, ed. (Springer-Verlag, New York & Heidelberg, Berlin 1973). Dye Lasers also provides detailed discussions on the principles of dye laser operation and the theory and structure of laser dyes.
Liquid organic dye lasers offer a number of advantages over gas or solid state lasers. One advantage is that a large number of organic lasing dyes are available that cover a broad range of the electromagnetic spectrum (near UV to near IR). Moreover, the dye lasers may be tuned by such means as varying the concentration of dye or replacing one of the reflecting ends of the laser cavity with a diffraction grating. Dye lasers also offer the advantage of being more economical. Finally, the liquid dye lasers will not crack as do solid lasers.
There is considerable interest in the development of high efficiency organic dyes for high energy dye lasers operating in the blue-green spectral region around 480 nm for applications which involve underwater communications, surveillance, viewing, range gating, etc. These laser dyes should show high photochemical stability even when high energy flashlamp excitation is used to stimulate laser emission from the dyes.
Only a small portion of the broad band radiation from flash lamps is absorbed by most state-of-the-art laser dyes. The unabsorbed radiation is lost by thermalization within the optical cavity of the laser. Unfortunately, the refractive indexes of most solvents are sensitive to temperature change. H.sub.2 O and D.sub.2 O are preferred because of their large heat capacities and small variation of refractive index with temperature changes. Additionally, H.sub.2 O and D.sub.2 O have good photostabilities and are nonflammable. Therefore, it would be particularly desirable to find photochemically stable, high efficiency laser dyes which are soluble in water.